The subject matter disclosed herein generally relates to fuel tank inerting systems for aircraft and, more particularly, to fuel tank inerting systems configured to supply inert gas in an aircraft.
In general, aircraft pneumatic systems including, air conditioning systems, cabin pressurization and cooling, and fuel tank inerting systems are powered by engine bleed air. For example, pressurized air from an engine of the aircraft is provided to a cabin through a series of systems that alter the temperatures and pressures of the pressurized air. To power this preparation of the pressurized air, generally the source of energy is the pressure of the air itself.
The air bled from engines may be used for environmental control systems, such as used to supply air to the cabin and to other systems within an aircraft. Additionally, the air bled from engines may be supplied to inerting apparatuses to provide inert gas to a fuel tank. In other cases, the air may be sourced from compressed RAM air.
Regardless of the source, typically the air for fuel tank inerting is passed through a porous hollow fiber membrane tube bundle known as an “air separation module.” A downstream flow control valve is controlled or passively operated to apply back pressure on the air separation module to force some amount of air through the membrane as opposed to flowing though the tube. Oxygen passes more easily through the membrane, leaving only nitrogen enriched air to continue through the flow control valve into the fuel tank. Typically air separation modules employ a dedicated ram air heat exchanger in conjunction with a bypass valve.